The invention relates to processes used in the manufacture of generally electrically nonconductive articles which include an electrically conductive surface layer, such as electrical connectors having a conductor pattern defined on the connector""s relatively resilient, electrically nonconductive substrate.
The prior art teaches.the manufacture of electrical connectors featuring a molded relatively resilient, electrically nonconductive, typically plastic substrate whose surface is coated with an electrically conductive, typically metallic layer, as through an electrolytic or chemical vapor deposition process. Such prior art processes typically require the masking, etching and plating of the substrate, or the deposition of multiple surface layers, or other equally time-consuming and costly process steps.
Alternatively, the prior art teaches the manufacture of electrical connectors using an insert molding process, wherein a metallic insert is placed inside a mold cavity, whereupon the connector""s plastic housing is molded surrounding the insert to obtain the connector. And, in yet another prior art process, a plastic connector substrate is separately molded in a single-shot process, whereupon metallic contacts are mechanically inserted into interference fit with suitable recesses molded into the plastic substrate. These alternate prior art processes are similarly characterized by relatively slow production rates and high manufacturing costs due to the high degree of precision mechanical manipulation required to assemble each connector.
The prior art also teaches a two-shot injection molding process for making an electrical connector, in which a platable resin is first molded, and then a second nonplatable polymeric resin is over-molded onto the first platable resin. A layer of an electrically conductive material is thereafter plated onto the platable resin, with the nonplatable resin itself acting as a plating mask.
The prior art teaches a similar type of two-shot injection molding process for making two-color plastic typewriter keys. In a first approach, the key""s exterior.surface or xe2x80x9cshell,xe2x80x9d including a void in the shape of the desired key character, is first molded in what is generally known as a xe2x80x9cshell-firstxe2x80x9d two-shot injection molding. More specifically, in a typical prior art shell-first molding process for making a shell-first article, the first shot forms the article""s shell and character voids using a first of two male dies and one female die. The first male die is then withdrawn from the shell, whereupon the shell is held by the female die as a second, somewhat smaller male die is mated with the female die. The second shot then fills the inside of the article, i.e., molds the article""s core as well as the character voids, with a different color material.
Alternatively, a key is molded xe2x80x9ccore-firstxe2x80x9d by means of a single male die which is used with a first-shot female die. The first female die-is then withdrawn, leaving the key""s core on the male die. The key""s core includes the key""s character as a raised surface. The male die is now mated with a somewhat larger second female die, and a second-shot forms the key""s shell. The over-molded shell thus surrounds, but does not cover, the key""s raised character. The use of rotary, movable and reciprocating mold dies to facilitate two-shot molding is also known in the prior art.
What is still needed, however, is a method of making an article, such as an electrical connector, which includes an electrically conductive surface layer over a relatively resilient, electrically nonconductive substrate, which features a mechanical interlock between the surface layer and the substrate to improve performance and, preferably, whose surface layer is of variable thickness to provide enhanced mechanical properties.
Accordingly, an object of the invention is to provide a method for making articles having an electrically conductive conductor pattern on at least one surface thereof, such as electrical connectors, featuring lower cost and less complexity in comparison with known methods.
Under the invention, a method for making an article having an electrically conductive conductor pattern on at least one surface thereof includes: injection molding a first one of the group consisting of a substrate and a surface layer; and injection molding a second one of the group consisting of a substrate and a surface layer, the second one being over-molded on the first one, wherein the substrate is molded of an electrically nonconductive material and the surface layer is molded of an electrically conductive material, and wherein the second one is over-molded on the first one.
In accordance with the invention, while the first and second materials are any electrically nonconductive and electrically conductive materials suitable for use in an injection molding process, in a preferred embodiment, the first material is preferably a relatively resilient polymer or xe2x80x9cplastic,xe2x80x9d such as a 6/6 nylon or a thermoset plastic, and the second material is preferably a tin-based or copper-based alloy. And, where the electrically conductive material is a metal which is first injection-molded, the metal has a higher melting point than the softening point of the plastic. Alternatively, where the metal is over-molded on the injection-molded plastic substrate, an exemplary method preferably further includes slightly melting the molded plastic substrate when injection-molding the metal surface layers.
In accordance with another feature of the invention, an exemplary method for making an article having an electrically conductive conductor pattern on at least one surface thereof preferably includes defining a first mold cavity between a first and second mold die, the first mold cavity being characterized by a variable spacing between the first and second mold dies; and injection molding the first one into the first mold cavity to obtain a first molded portion of the article, the first molded portion includes at least one surface feature. The method further includes removing the second mold die; defining a second mold cavity between the first mold die and a third mold die, a portion of the second mold cavity being bounded by the at least one surface feature of the first molded portion; and injection molding the second one into the second mold cavity to obtain a second molded portion of the article, the second molded portion including at least one surface feature complementary to the at least one surface feature of the first molded portion to thereby mechanically interlock the second molded portion with the first molded portion.
Still further, in accordance with yet another feature of the invention, the at least one surface feature of the second molded portion formed during the second injection molding step completely penetrates through the at least one surface feature of the first molded portion.
In accordance with another feature of the invention, the resulting connector advantageously includes a metallic surface layer of varying thickness with which to define the conductor pattern, with the metallic surface layer being mechanically interlocked with the plastic substrate to improve connector reliability and performance. And, because the preferably nylon substrate is relatively resilient, the resulting connector advantageously accommodates minor misalignment of the mating connector pins and sockets without breaking.